This invention relates to an ozone generator.
A conversion cell for generation of ozone generally comprises two electrodes having an insulator therebetween. The insulator does not occupy the entire space between the confronting surfaces of the electrodes, but a gas space is left between the insulator and one of the electrodes. The gas space has an inlet port and an exit port. The inlet port is connected to a source of a feed gas under pressure and the outlet port is connected to a volume at lower pressure than the supply pressure of the feed gas. Accordingly, the feed gas, which contains oxygen, flows through the gas space. The electrodes are normally of approximately equal surface area, and an alternating potential of 5 kv or more and a frequency of 0.05-3 kHz, is established between the electrodes, for example by connecting the electrodes to opposite ends of the secondary winding of a transformer, the primary winding of which is connected to an alternating current source at a considerably lower voltage. A corona discharge is established in the gas space. Some of the oxygen molecules present in the gas space disassociate into atoms, and some of the oxygen atoms combine with oxygen molecules to create ozone molecules.
It is desirable that the ozone remain at a relatively low temperature, because at temperatures above about 48.degree. C. an ozone molecule readily disassociates into an oxygen atom and an oxygen molecule, and there is a high probability that oxygen atoms will recombine to form oxygen molecules. A large proportion (80% to 90%) of the electrical energy supplied to the conversion cell of a conventional ozone generator is not utilized directly in the conversion of oxygen to ozone, and this excess energy is dissipated as heat. One mechanism for generation of heat is the rapid reversals of electrical stress applied to the dielectric and the gas present in the gas space. Most conventional ozone generators require liquid cooling or a refrigeration system to remove the heat generated by the excess energy supplied to the conversion cell.
Using oxygen as the feed gas, the gas supplied at the outlet of an ozone generator that is currently available may contain up to about 2% by weight ozone. Because of the input energy required and the resulting generation of heat, few conventional ozone generators are able to generate continuously a gas mixture containing more than 2% by weight ozone.
U.S. Pat. No. 4,869,881 (Collins) discloses an ozone generator in which a silicon controlled rectifier (SCR) is connected in parallel with the primary winding of a transformer the secondary winding of which is connected to the electrodes of the conversion cell. The SCR is repeatedly fired in order to chop the DC voltage provided by a power supply into pulsed DC voltage. The frequency at which the SCR is fired is controlled by a potentiometer.
U.S. Pat. No. 4,128,768 (Yamamoto et al) discloses an ozone generator in which silicon controlled rectifiers are used to convert a direct current supplied by a power supply to alternating form for application to the primary winding of the transformer.
In accordance with the disclosure of Yamamoto et al, the voltage applied to the electrodes of the conversion cell varies cyclically, and as the potential difference between the electrodes increases, the potential difference across the gas space increases to a threshold value, at which discharge takes place, and immediately falls to zero, and this cycle repeats several times within each cycle of the alternating voltage between the electrodes.
U.S. Pat. No. 1,845,670 (Lebrun) discloses a transformer-driven ozone generator.
U.S. Pat. No. 4,410,495 (Bassler et al) discloses an ozone generator having a cylindrical conversion cell in which the outer electrode is composed of multiple sleeves spaced apart along the cell. The sleeves are connected through respective switches to an alternating current source.
U.S. Pat. No. 4,603,031 (Gelbman) discloses a cylindrical conversion cell in which the gas space is defined between the insulator and the exterior surface of the inner electrode, and the inner electrode is apertured. Feedstock gas is supplied to the gas space by way of the interior of the inner electrode and the apertures in the inner electrode.
U.S. Pat. No. 4,690,803 (Hirth) discloses an ozone conversion cell in which the gas space is defined between the exterior surface of the insulator and the interior surface of the outer electrode. The insulator is carried by the inner electrode and is provided with a protective layer of passivating glass.
U.S. Pat. No. 4,966,666 (Waltonen) discloses a cylindrical conversion cell in which the insulator is in the form of a rod having a helical groove at its exterior surface, and the groove constitutes the gas space to which feedstock gas is supplied. It will be recognized by those skilled in the art that a gas space in the form of a helical groove provides a long dwell time for the feedstock gas in the conversion cell.